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HomeMy WebLinkAboutCDP 07-12; SEARS RESIDENCE; GEOTECHNICAL UPDATE; 2015-12-16CD? 07—Li HETHERI.NGTON ENGINEERING, INC. SOIL & FOUNDATION- ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY December 16, 2015 Project No. 7842.1 Log No. 18063 Mr. Tom Sears 1387 Cynthia Lane Carlsbad, California 92008 Subject: GEOTECT-INICAL UPDATE Proposed Single-Family Residence 4015 Sunnyhill Drive Carlsbad, California DEC 052016 References: Attached Dear Mr. Sears: In accordance with your, request, Hetherington Engineering, Inc. has performed a geotechnIcal update for a proposed single-family residence at the subject site. Our work was performed in December 2015. The purpose of the update is to provide grading and foundation recommendations, and seismic design criteria consistent with the 2013 California Building Code With the above in mind our scope of work included the following: Research and review of available plans and geologic literature, pertinent to the site vicinity (see References). Engineering and geologic analysis. Preparation. of this report providing. out conclusions and recommendations. Our prior "Geotechnical Investigation..." (Reference 1) should be reviewed for the results of field and laboratory work previously performed and conclusions/i ecomrnendations that are not revised or duplicated in this report PROPOSED DEVELOP'ffiNT We understand that the proposed constniction consists of a two-story, partial subterranean single-family residence with attached garage and retaining walls up to 6-feet high We anticipate the structure will be of relatively, light masonry and wood-frame construction, founded on conventional continuous/spread footings with slab-on-grade ground floors Proposed grading consists of cut and fill up to 6-feet / ) 5365 Avenida Encinas, Suite A • Carlsbad, CA 92008-4369 • (7 60) 931-1917 • Fax (760) 931-0545 327 Third Street • Laguna Beach, CA 92651-2306 • (949) 715-5440 • Fax (949) 715-5442 wwwhetheringtonengineering.com fl GEOTECHNICAL UPDATE Project No. 7842.1 Log..No. 18063 December 16, 2015 Page 2 SEISMICITY The site is located within the seismically active southern California region. There are, however, no known active oi potentially active faults presently mapped that pass through the site nor is the site located within the presently defined limits of an Alquist-Piiolo Earthquake Fault Zone Active or potentially active fault zones within the site region include the Rose Canyon and Elsinore (Julian Segment) Strong ground motion could also be expected from earthquakes occurring along the San Jacinto and San Andreas fault zones, which he northeast of the site at greater distances, as well as a number of other offshore faults. The following table lists the known active faults that would hay.e the most significant impact on the site: Maximum Probable Fault Earthquake Slip Rate Fault (Moment Magnitude) (mm/year). Type Rose Canyon (9-kilometers/6-miles SW) 7.1 1.5 B Elsinore (Julian Segrnent (37-kilornetcrs/23-miles NE) 7.3 3 A SEISMIC EFFECTS 1, Ground Motions The most significant probable earthquake to effect the property Would be a 7.1 magmtude earthquake on the Rose Canyon fault zone Based on Section 1803 5 12 of the 2013 California Building Code, peak ground acceleiations modified for site conditions (PGAM) of 0.464g are possible for the design earthquake 2. Landsliding The subject property has, no previously mapped ancient landslide deposits. Due to the relatively level topography of the site, the potential for future landsliding to occur is considered to 'be' very low. HETKEINGTOII ENGINEERING, INC. . GEOTECHNICAL UPDATE Project No. 7842.1 Log No. 18063 December 1.6, 2015 Page 3'. Ground Cracks The risk Of faUlt surface rupture due., to active faulting is considered low due to the absence of an active fault on site Grobnd cracks due to hakmg fioni seismic events in the.gion.Eire possible, as .w.ithafl.oflsouthem California. Liquefaction The risk of seismically induced liquefaction within the site is considered low due to the 1 acicof shallow groundwater and-the dense nature Of the under-lying materials. 5, Tsunamis. The risk for seismically generated ocean waves to affect the site is considered low to dueto the site elevation. CONCLUSIONS AND RECOMMENDATIONS 0 1. General The proposed -develcpmentis considéred:feasiblefrom. a geotechnical standpoint. Giading and foundation plans should take into account the appiopriate geotechmeal features of the site The pioposed construction is not anticipated to adversely impact the adjacent prçperties from a geotechnical standpoint provided the recommendations presented in this report and good constiuction practices are implemented during design and construction. 2. Seismic Parameters for Structural Desian Seismic considerations 'that should be used for sfructuial design at the site, based on Section 1613 of the 2013 California Building Code and ASCE 7-10, include the following: a. Ground Motion - The proposed structure, should be designed and constructed to resist the effects of seismic ground motions as piovided in Section 1613 of the 2013 Califonil:aTBuilding Code. Site Address: 4015 Sunnyhill Drive, Carlsbad, California, Latitude: 33.155 Longitude: -1.17.322 S HETHEINGTON ENGINEERING, INC. S . GEOTEcHNICAL UPDATE Project No. 7842.1 Log No. 18063 December 16,2015 Page 4 b, Spedfral Reponse Accelerations Using the location of the property and data obtained from the U S G S Earthquake Hazard Program, short peuod Spectral RespöeAcceieiations S (0.2 second period) ad S (1.0 decohdperiod) are: * S1.114g 81 0.428g C, Site Class - In accordance with Chapter 20 of ASCE 7-10 and the underlying geologic conditions, .a Site Class D is considered appiopnate for the subject property.- Site Coefficients. Fii4 F, -.In .pcordaice with Table 1613.3.3 and considering the values 'of S and S1,'SiteCoefflcients are: F= 1..O54 F, 1.572 .pectra1 Response Acceleration Parameters Sni and Srn - In accordance with Section 16133.3 and considering the values of S and S1, and F8 and Fv, Spectral Response Acceleration Parameters for Maximum Considered Earthquake are: S .Sm5= (Fa)(Ss) = 1.175g Smj = (F)(Si) = 0.673g Design Spectral Response Acceleration Parameters Sda and Sd1 - In accordance with Section 1613 3 4 and considering the values of Sin, and Smi, Design Spectral Response Acceleration Parameters for Maximum Considered Earthquake are: Sd2/3Sm 0.783g Sd1 2/3 Smj = 0.449g Lona Period Transition Period - A Long. Period Transitional Period of TL 8 seconds, econd is provided for use in San Diego County. Seism.ic.Design Category - In accordance with Tables 1604.3, and 1613.3.5.2 and ASCE 710, a Risk Category II and a Seismic Design Category D are considered appropriate for the subject property. 3. SigpeSt4bilfty The site is relatively level and no significant cut or fill slopes are proposed. S HETHERINCTON ENGINEERING, W.C. O GEOTECHNICAL UPDATE Project No. 7842.1 Log No. 18.063 December 16, 2015: Page 5 4, Site Grading Clearing and }rubbing - Existing improvement, vegetation and miscellaneous debris should be removed to an appropriate offsite disposal atea Holes resulting fiom the iemoval of buried obstructions which extend below finished site grades, should be replaced with compacted fill or lean concrete, In the event that abandoned cesspools, septic tanks of. stoiage tanks are discoveied during the excavation of the site, they should be removed and backfilled in accordance with local iegulations Existing utility lines to be abandoned should be removed and capped in accordance with local requirements. Removal of Unsuitable Soils Within the limits of the proposed grading and improvements and to 3-feet beyond, where possible, existing fill, topsoil and disturbed terrace deposits and other unsuitable soils should be removed to appioved terrace deposits Removal depths of 2 to 4-feet below existing site grades are anticipated. The actual depths and extent of removals should be determined by the Geotechnical Consultant during site grading. Scarification - All areas to receive fill should be scarified to a minimum depth of 6 to 8-inches, brought to near optimum moisture content, and compacted to at least 90-percent relative compaction based upon ASTM: D 1557. Compacted Fill - Fill soils should be moisture conditioned to about optimum moisture content and compacted by mechanical means in uniform horizontal lifts of 6 to 8-inches in thickness. All fill should be compacted to a minimum relative compaction of 90-percent based upon ASTM: D 1557. The on-site materials are suitable for use as compacted fill Rock fragments over 6-inches in largest dimension and other peiishable or unsuitable materials should be excluded from. the fill. All grading and compaction should be observed and tested by the Geotechnical Consultant. Any imported soil should have a very low expansion potential and should be approved by the Geotechnical Consultant prior to import. 5. Foundation and Slab Recommendations The proposed building may be supported on conventional continuous/spread footings founded at least 18-inches below lowest adjacent grade and bearing in compacted fill and/or terrace. deposits. Continuous footings should be at least 12-inches wide and reinforced with a minimum of four #4 bars, two top and two bottom. Foundations located adjacent to utility trenches should extend below a It 1 plane projected. upward from the bottom of the trench. HETHEHGTON E1UGNEEPING, INC. . OEOTECHNIAL UPDATE Project No. 7942.1 Log No. 18063 December 16, 2015 Page 6 Foundations bearing as recommended may be designed for a dead plus live load bearing value of 2000-pounds-per-squaie-foot This value may be increased by one- thud for loads including wind and seismic foices A latetal bearing- value of 250- pounds-per-squat e-foot pei foot of depth to a maximum value to 2000-pounds-per- square-foot and a coefficient of friction between foundation soil and concrete of 0.35 may be assumed These values assume that footings will be poured neat against compacted fill 01 terrace deposits Foormg excavations should be observed by the Geotechrucal Consultant prior to the placement of reinforcing steel in order to verify that they are founded in suitable bearing materials. Slab-on-grade floors should have a minimum thickness of 5-inches (actual) and should be rein-forced with #4 bars spaced at 18-inches, ccntei-to-centei, in two directions, and supported on chairs so that the reinforcement is at mid-height in the slab Floor slabs, including the garage, should be underlain with a moisture vapor retarder consisting of at least a 10-triil polyethylene membrane At least 2-inches of sand should be placed over the vapor retarder to assist in concrete curing and at least 2-inches of sand should be placed below the vapor retarder. The vapor retarder should be placed in accordance with ASTM: B 1643. Prior to placing concrete, the slab subgrade soils should be thoroughly moistened, Vapor retarders are not intended to provide a waterproofing functinn. Should moisture vapor sensitive floor coverings be planned, a qualified consultant/Contractor should be consulted to evaluate moisture vapor transmission rates and to provide recommendations to mitigate potential adverse impacts Of moisture vapor transmissions on the proposed flooring. 6. Retaining Walls Retaining wall foundations should be designed in accordance with the foundation iecommendations provided previously in this report. Retaining walls flee to rotate (cantilevered walls) should be designed for an active piessure of 35-pounds-pei- oubic-foot (equivalent fluid pressure) for level backfill consisting of the on-site granular soils, Walls restrained from movement at the top should be designed for an at-i est pressure of 60-pounds-per-cubic-foot (equivalent fluid pressure) for level backfill consisting of the onsite soils. Any additional surcharge pressures behind retaining walls should be added to these values. Retaining walls should be provided with adequate drainage to prevent buildup of hydrostatic pressure and should be adequately waterproofed. The subdiain system behind retaining walls should consist of at least, a 4-inch diameter Schedule .40 (or HETHERNNGTON ENGINEERING,, INC. . GEOTECHNICAL UPDATE Project No. 7842.1 Log No. 18063 December 16, 2015 Page 7 equivalent) perforated (perforations "down") PVC pipe embedded in at least 1-cubic- foot of 3/4-inch crushed iock per lineal foot of pipe all wiapped in approved filter fabric Other subdram systems that may be contemplated for use behind the retaining walls due to the ultimate wall designs and construction methodology will be addressed on a case-by-case basis Recommendations for wall water roofing should be provided by the Project Architect and/Or Structural Engineer. The lateral pressure on retaining walls due to earthquake motions (dynamic lateral force) should be calculated as PA = 3/8 H2kh where PA = dynamic lateral force (lbs/ft) ly = unit weight = 120 pcI H = height of wall (feet) Ich seismic coefficient 0.15 The dynamic lateral force is in addition to the static force and should be applied using . a triangular distribution with the resultant applied at 1/311 above the base of the wall Retaining wails that are less than 6-feet high do not require design to resist the additional earth pressure caused by seismic ground shaking. Trench and Retaining Vail Backfill All retaining wall and utility trench backfilJ, should be compacted to at least 90 percent relative compaction (ASTM: D 1557). Backfill should be tested and observed by the Geotechnical Consultant. Hardscap Concrete flatwork should be at least 5-inches thick (actual) and reinforced with No. 4 bars spaced at 18-inches on-center (two directions) and placed on chairs so that the reinforcement is in the center of the concrete Contraction joints should be provided at 8-feet spacing (maximum) Joints should create square panels where possible For rectangular panels (where necessary) the long dimension should be.no more than 1.5 times the short dimension Joint depth should bel at least 0.25 times the flatwoik thickness Expansion joints should be thoroughly sealed to prevent the infiltration of water into the underlying soils. HETHERINGTON ENGINEERING, INC. S GEOTECHNIAL UPDATE Project No. 7842.1 Log No, 18063 December 16 2015 Page 8 Temporary Excavations Temporary excavations may be made up to 5-feet vertically in the terrace deposits And at a 11 (horizontal to vertical) above 5-feet Field observations by the Engineering Geologist during excavation of temporary slopes are recommended and considered necessary to confirm anticipated conditions and proVide revised recommendations, if warranted, Drainage The following recommendations are intended to minimize the potential adverse effects of water, on the structure and appurtenances. a, Consideration should be given to providing the structure with roof gutters and downspouts that discharge to an area drain system and/or to suitable locations away from the structure. b. All site drainage should be directed away from the structure. No landscaping should be allowed against the structure. Moisture accumulation or watering adjacent to foundations can result in deterioration of building materials and may affect the performance of foundations. Irrigated areas should not be over-watered. Irrigation should be limited to that required to maintain the vegetation. Additionally, automatic systems must be seasonally adjusted to n'nmniize over-saturation potential particularly in the winter (rainy) season. All yard and roof drains should be periodically checked to verify they are not blocked and flow properly, and maintained as necessary. 11. Recommended Observation and Testing -During Construction. The following, tests and/or observations by the Geotechnicai Consultant are recommended: Observation and testing during site grading. Observation of foundation excavations prior to placement of forms and reinforcement, Retaining wall backdraiiis. HETHERINGTON ENGINEERING, INC.. . GEOTECHNICAL UPDATE Project No. 7842.1 tog No. 18063 December 16, 2015 Page 9 Utility trench and retaining Wall bac1fill, Hardscape siibgrade. 12. Grading and Foundation Plan Review Grading and foundation plans should be reviewed by the Geotecl-iriical Consultant to confirm conformance with the recommendations presented herein or to modify the recommendations as necessary. LIMITATIONS The analyses, conclusions and recommendations contained 14 this report are based on site conditions as they existed at the time of our investigation and further assume the excavations to be representative of the subsurface conditions throughout the site If different subsurface conditions flom those encountered during our exploration are observed or appear to be plesent in excavations during construction, the Geotechrncal Consultant should be promptly notified for review and reconsideration of recommendations. Our investigation was performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable Geotechnical Consultants practicing in this or similar localities No other warranty, express or implied, is made as to the conclusions and professional advice included in this report. This opportunity to be of service is sincerely appreciated.. If you have any questions, please call this office. Sincerely, uBTHER...'GjNEERING, INC. Civil Engineer 3048 Geotechuical Engin (expires 3/31/16) No.391 Distribution:. 1 -via e-mail aul A. Professional Geologist 3772 Certified Engineering Geolo Certified Flydrogeologist 59 (expires 3/31/1 6) S HETHRINGTON ENGINEEPNG, INC. REFERENCES Hetherington Engineering, Inc. "Geotechnical Investigation, Proposed Single-Family Residenôe, 4015 Sunnyhill Drive, Carlsbad, California," dated September 18, 2007. Hetherington Engineering, inc., "Grading Plan Review, Proposed Single-Family Residence, 4015 Sunnyhill Drive, Carlsbad, California,".dated January 23, 2009; ICBO, "California Building Code," 2013 Edition, 4. USGS —US Seismic Design Maps. Project No. 7842.1 LôgNo. 18.063 HEThEINGTON ENGINEERING, INC.